Exploring Salt and Solvent Effects in Chloride-Based Electrolytes for Magnesium Electrodeposition and Dissolution

We describe in this work Mg electrodeposition and dissolution from a wide range of inorganic ethereal electrolytes consisting of MgCl2 and a second chloride salt. Systematic variations of the cosalt reveal two broad classes of electrolytes, namely, the group 13 electrolytes, which require electrolytic cycling to improve their performance, and electrolytes based on heavy p-block chlorides, which exhibit Mg intermetallic formation. Results from electrospray ionization mass spectrometry demonstrate that Mg deposition and stripping only occur in electrolytes containing Mg multimers. We also explore the role of solvent in determining the electrochemical performance of chloride-based electrolytes. Our analysis establishes thermodynamic parameters that dictate the ability of a solvent to support Mg electrochemistry in the MgCl2-AlCl3 system. In their totality, these results illustrate important electrolyte design guidelines for future Mg-ion batteries.